Pulse widener and marker separator



Q OM QL Lfxl July 10, 1951 L. DUBIN 2,559,606 r PULSE WIDENER AND MARKERsEPARAToR Filed July 21, 1948 [NVEN TOR. 5575/? DUB/N )erro/PNE?Patented July 10, 1951 2,559,606 PULSE WIDENER AND MARKER SEPARATORLester Dubin, Brooklyn, N. Y., assignor to International StandardElectric Corporation, New York, N. Y., a corporation of DelawareApplication July 21, 1948, Serial No. 39,967

2 claims. (o1. 179-15) This 4invention relates to multichannel receivingsystems and more particularly to means for Vwidening the transmittedpulses upon reception I and for separating synchronizing pulses fromintelligence signal pulses.

One of the objects of the invention is to provide a method and means forWidening such pulses as are used in a so-called pulse time modulationsystem.

Another object is to provide means for separating the modulation pulsesfrom the synchronizing pulses in a multichannel system of reception.

Still another object of my invention is to provide a circuit arrangementwhich is adapted for use in connection with a demodulating system of thetype wherein signals are composed of time displaced lpulses representingamplitude variations of the intelligence signals.

In a so-called pulse time modulation system of intelligence transmissionwhich is also a multiplex system, it is desirable to secure a greaterinitial energy output to lengthen the eiects of the transmitted pulses.The pulses as received are of the order of one-half a microsecond induration to permit channel spacings which will serve to reducecross-talk, but for the sake of improved eficiency in the demodulationprocess the received pulses should be of greater time duration, forexample, of the order of 1 microsecond. So, upon reception, thereceiving equipment must be capable of widening the received pulses toan equivalent length, say of 2 microseconds duration. According to myinvention I accomplish this result by widening the keying pulse uponreception.

In carrying out my invention I cause the intelligence signals composedof keying pulses to be widened by the use of passive circuits which arenegligibly subject to cross-talk. According to a feature of my inventionthis Widening is accomplished by passing the received pulse trainsthrough two parallel circuits one of which introduces a delay signal tothe pulse duration desired. The pulses of these trains are then used inconjunction with a storage circuit to accomplish the desired broadening.In accomplishing this result I obtain a further advantage in that thecircuit arrangement provides for the separation of a synchronizing pulsefor purposes of timing the sweep circuit generator for the cathode raytube.

My invention will now be described in more detail, reference being madeto the accompanying drawing in which- Fig. 1 shows a circuit diagramincluding essential components for carrying out the invention accordingto one exemplary embodiment; and

Fig. 2 shows by way of illustration certain graphs of the signals and ofthe demodulation effects, these graphs being used to explain theoperation of the system of Fig. 1.

As a preface to the detailed description of my invention it may be Wellto refer briefly to the prior art as a background for systems whichutilize the pulse time modulation method. These systems, generallyspeaking, are so organized that the intelligence may be transmitted by aseries of pulses for each channel, the pulses being displaced inaccordance with the amplitude of the modulation. For example, if therewere no modulation, the pulses would be spaced equidistantly in point oftime. For a given amplitude of the modulation signal the pulse isdisplaced and the degree of time displacement corresponds to theamplitude. Where a number of channels of communication are to bemultiplexed, each channel is represented by a train of pulses which areinterwoven with the pulses of other channels.

The receiving equipment may be provided with an electron beamdistributor tube having a series of targets for separation of thesignalsinto their respective channels. The tube may be provided withbeam deecting circuits of the type which produce rotary scanning. On theother hand, the scanning principle may be the same as is commonly usedfor television. For purposes of illustration I have shown herein arotary scanning method. I do not intend, however, to limit the use ofthe invention to such a method.

In a copending application filed by E. Labin and D. Grieg, Serial Number565,152, led No vember 25, 1944, there has been described a re.- ceivingsystem which deals with demodulation of transmitted pulse timemodulation signals. In that application there was shown and described acathode ray tube having a plurality of targets for impingement of theelectron beam in order to separate the signals. The targets fordifferent channels were disposed behind an orilced screen. The scanningmeans produced rotary beam deflection. The incoming signals consisted ofintelligence signals for each channel and a periodic synchronizing pulsewhich was differentiated from the intelligence signals by being oflonger duration. The means provided for separating the synchronizingsignals from intelligence signals need not be herein discussed since Ihave adopted alternative means. This matter will be better understoodafter describing the'.

electron discharge tubes 2 and 3. The coupling means may be, forexample, capacitors 4 and 5 respectively. The tubes 2 and 3 are shown byway of example to be pentodes. Other types of tubes may be adopted ifpreferred.

The input circuits for tubes 2 and 3 are conventional in that theyinclude resistors El con nected between the control grid and ground. Thecathode of tube 2 has a resistor 'i connecting it to ground. The cathodeof tube 3 is directly grounded. Screen grid potential is supplied from asource indicated as +B connected to the different screen grids by way ofresistors 8 and 9 respectively. These screen grids are shown havingby-pass capacitors Il) coupling them to ground. Resistors 8, I I and 1are interconnected as a voltage divider between the plus and minusterminals of the B source, the minus terminal being understood to begrounded. Resistor II forms an interconnection between the cathode andthe screen grid in tube 2.

The anode in tube 2 is supplied with positive potential from the +Bterminal through a re sistorv I2. This anode isalso connected to thecathode of a diode discharge tube I3, and is further connected lto othercomponents, as will be hereinafter mentioned. The anode of tube i3 isconnected to the +B source through a resistor I4. The anode of tube I3is also connected directly to the anode of another pentode tube IE.

The output from tube 3 is applied to the input of delay network I6.Output potentials from the delay network I3, which are phase-displacedwith respect to the output from tube 3, by an amount equal to thedesired widening are applied to the control grid of tube I5. The anodesof tubes I5 and i3 are interconnected. Negative pulses from tube 2 tendto build up a negative potential in storage capacitor II, while theposin tive pulses applied to diode I3 from the output of tube I5 tend todischarge capacitor I?. Resistor 4I is of suiiiciently high value as tohave a negligible shunting effect on condenser G8. The result iseiectively to broaden the keying pulses which constitute the incomingsignals ti' a value corresponding with the delay in netn work I6. Othercircuit components of tube I are conventional. They include a biasingresistor I8 for the screen grid, and a by-pass capacitor ISIV couplingthe screen grid to ground. The cathode resistor 29 shunted by acapacitor 2I aiords a ground connection for the cathode.

Variations of potential across capacitor il are utilized in two unitswhich are connected to it in parallel, one of these units being a linearampli fier 22 and the other being a clipper amplifier 23. The outputfrom the linear amplifier is fed to a marker pulse selector 24 whichselects the marker or synchronizing pulses for causing a 2- phasegenerator to be locked in step. The unit 24 responds only to the markerpulses because they are of longer duration. Unit 23 delivers its outputto Z-phase generator 25 from which deiiecting circuit potentials areobtained in 9G phase displacement for purposes of rotary scan-- ning.Oneof the output conductors from unit 25 leads to a beam dei'iectorelectrode 26. Another such output conductor leads to a beam deflectorelectrode 2. Electrode 26 is capacitively associated with a groundedelectrode 28, electrode 2T being likewise capacitively associated withgrounded electrode 25. The neutral point in the phase splitting circuitof the generator is also grounded.

The deecting electrodes 26, 27, 28 and 29 are built into a cathode raytube 30 having the usual electrodes for forming an electron gun. Thecomponents of the gun include a cathode 3l and focusing electrode 32.Intervening between the cathode and the focusing electrode 32 is acontrol grid 33. For one embodiment of the invention the grid 33 has asuitable cut-01T bias as obtained from a direct current source 34 con-vnected through a resistor 35. Signals are applied to the control grid 33through a capacitor 3G coupled to the output from the clipper amplifierunit 23. The input side of unit 23 is connected to the anode of tube 2as before stated.

A plurality of targets or output electrodes 31 is mounted at the largeVend of the cathode ray tube in opposition to the electron gun.Intervening between the gun and the targets a mask or aperture plate isalso provided. This mask is not delineated except by broken lines whichoutline certain orifices therein asv at 3B.

Before explaining the principlesV of operation of my invention, itshould be understood that,` according to the prior art, demodulation ofsignals by means of a cathode ray tube such as that herein shown as tube30 is somewhat as follows:

The beam, in its movement, is caused to either traverse the targets orto move along a path adjacent the same. The time modulated pulse en-`ergy may be used to. control coaction between the beam and each targetor responsive device in any one of several ways. This coaction betweenthe beam and' the responsive devicesy causes a iow of energy in thechannelA receiving circuit associated with each device, the amplitude ofsuch energy being proportional to the time modulationof the pulses ofthe corresponding channel. According to one feature of the prior artinvention, the coaction between the beam and the respon sive devices iselected bykeying the beam onand ol according to the leading and trailingedges of. the pulses. Where, this type of control is em ployed, thebeamY sweep is caused to traverse successively the same responsivedevices during the rsame corresponding parts of itscyclic movement,

whereby the keying on and off of the beam inA relation to such partscontrols the coaction referred to.

According to another feature of the` prior art invention, the controlof. the coaction between the beam and the sensitive devices is effectedby deecting the beam according to the pulse energy. For example, thebeam is caused normally to sweep, in the absence ofsignal modu latedpulses, and at a given intensity, along a path adjacent the responsivedevices. When the beam is deilected by a channel pulse, it is caused tocoincide with one of the responsive devices for a time intervalproportionally to the degree of the time. modulation of the dellectingpulse energy, thereby producingk a corresponding ow of. energy in thereceivingA channel of the.

beam intercepting device.

This coaction, according to still another feature of the prior art`invention, may be effected by applying the pulse energy to av givenelement of each of the responsive devices whereby the devices are maderesponsive to the beam only when the pulse energy is applied to suchele.- ments. The beam in this case is maintained at a constant intensityand its path of movement is caused to coincide successively with theresponsive devices.

The displacement of the signal pulses in point of time causes a certainvariation of amplitude of output from the target 31 and, depends uponthe proportion of intercepted electrons to electrons which reach thetargets. If, thereiorepa signal pulse is applied to the control grid 331n the cathode ray tube at a time when the deiiect* ing circuits deectthe beam into a portion 0i its rotary orbit between the orifices of themask, few, if any, electrons will reach a target. If, however, timedisplacement causes the signals to be applied to the grid 33 when beamdeflection would permit the passage of the electrons through an orifice38. then the target 31 would receive sucient electrons to shift its biasin a negative direction. This effect, may, of course, be utilized ineach channel of a multiplex system where a separate target is providedfor each channel. The utilization means connected to each target are notherein shown, but they will be well understood as being of any suitabletype for the kind of intelligence that is to be received whether it bevoice signals or video signals or" a television system or facsimilesignals.

Coming now to a description of the mode of operation of my invention, itshould be borne 1n mind that the invention itself aims to widen theeffects of the received pulses and thus to enable the tube 39 tofunction with improved efficiency. This is only one advantageous resultto be obtained, however, because the circuit arrangement is adapted todiierentiate between signal pulses and marker pulses in an advantageousmanner. While I have illustrated only the type of circuit in'which thebeam is keyed on or oiT by the received pulses it should be clear thatthe advantages of pulse widening apply equally well to other type ofcircuits.

Referring to Fig. 2 and to curve a therein, this represents graphicallya typical incoming signal as it is amplied in the receiver unit I. Themarker signal is composed of two pulses which are included in the timerepresented by the bracket 39. The marker pulse is used forsynchronizing only. The curve a then continues with a series of pulses,each appropriate to a diierent multiplex channel. One of these pulses 40may occur before or after a moment that has a constant reference timerelation to the marker pulse 39. The phasal variation in the arrivaltime of the pulse 453 is what constitutes the modulation. Pulse 4lappropriate to a different channel may also vary in the instant ofarrival time with respect to the reference moment measured from themarker pulse.

As explained above, the instant of arrival of each signal pulse variesin accordance with the amplitude of the signal at a correspondinginstant and, therefore, demodulation of the signal is obtained byallowing more or less of the electrons from the electron gun to reachthe targets 31.

Curve b in Fig. 2 represents delayed inverted pulse train at the inputof tube I5. Tube I3 is subject to intermittent conductive action inresponse to the pulse of curve b, while the output pulses of curve aserve to build up a negative charge in condenser l1, thus producing auctuating charge on capacitor i1, timed with the incoming pulse trainproducing a resultant pulse train, as shown by curve c in Fig. 2. Thepulses 40, 4| etc. are thus widened as indicated at 45, 46 of curve c.These wider pulses have the eiect of releasing more energy at targets31, as illustrated, than would be produced by the narrower pulsesreceived. The double marker pulses like those bracketed at 39 and 42 areampliiied in the unit 22, producing a pulse of 6 greater' negativeamplitude as shown at 41'. After being appliedv to the marker pulseselector 24 they alone are' of sufficient amplitude to overcome thecut-off bias in marker pulseselector 24, indicated by the line 45, curvec. So these marker pulses are used to maintain synchronism intheoperation of the deilecting circuit generator 25. This unit 25 possessesa phase splitting means, or is any desired typev of Z-phase generatorwhich may be synchronized withthe separated marker pulses to deliversuitable poltentials for application to the beam deflecting electrodes26 and 21.

By way of illustrating the variable degree of collection ofA electronson the targets 31, as a function of the phase of displacement of thesignal pulses, curve c has been drawn through certain rectanglesA whichrepresent the targets. The phase, or time displacements of the' pulsesierefore produce' effects which correspondy to the amplitude variationsof the original modulations. The advantage to be derivedfrom theelongation of the pulses will be Abest understood by considering thatthe width of the incoming pulses such as represented at 40 or 4I may beso narrow as to cause a relativelyV short time of contact with thetargets. On the other hand, with elongation of theY signals, the energydelivered bythe electron beam as it strikes a target is eiective for agreater period than that of the incoming pulses. The target elementcorresponding to the marker pulse 39 may be eliminated as it is notneeded for synchronizing the sweep. The elongation of the pulses isuniform and does not vary with the phase displacement. This is becausethe delaying action of the network i6 is constant. This means that thetime relation between two pulse components 40 and 43 is a constant, andis equal to that between pulse components 4l and 44. The spacing betweenthe front slopes of the signal pulses varies, however, in accordancewith the modulation and thus provides the possibility for translation ofthe incoming signals into intelligence.

Although I have described my invention by reference to a particularembodiment thereof, it will be understood that variations may be made bythose skilled in the art without departing from the spirit and scope ofthe invention itself.

I claim:

l. A receiver for multi-channel pulse trains in which individual trainsof signal pulses, the pulses of each train being time displacementmodulated according to signals in different channels, are interleaved inthe form of a single multi-channel train with marker signals inserted atregular intervals in said multi-channel train, comprising means forreceiving said multi-channel trains, means for widening each of thepulses of said train while maintaining the time displacement modulationthereof, a cathode ray tube channel distributor and demodulator of thetype in which the signal pulses are applied to the grid thereof to keythe beam and in which the beam is cyclically deected with regularperiodicity, the cross section of the beam and the target elements beingso arranged that the time displacement of the pulses varies t l1e Aamount of electrons striking the target elements so that the energy inthe output of each of said target elements varies in accordance with thetime displacement modulation, each target element providing at itsoutput the pulses belonging to a separate channel, means for applyingthe widenedpulses to the grid of said cathode ray tube, means forselecting theA marker signal and means controlled by said marker signalfor regularly cyclically deflecting the' beam, said marker signals eachconsisting of two adjacent pulses spaced more closely together than anyother two pulses in said multi-channel train and said meansforseparating the marker signal and the means for widening the signalpulses comprising a storage device, means for applying each of thepulses of thevmulti-channel train to sequentially charge said device,means for delaying the multichannel train for a period greater than theperiodv between the two adjacent pulses of the marker signal and lessthan the period between any "other two pulses of the train, means forapplying the delayed pulses to each discharge said storage devicewhereby the periodic voltage built up on said storage device by themarker pulses'of the undelayed train. are greater than the-correspondingvoltage of the signal pulses, a threshold device coupled to said storagedevice having a threshold level above said corresponding voltage Yandbelow said periodic voltage whereby the marker signal is selected, andmeans couplingsaid storage device to the grid of said cathode ray tube.

v2. vIna channeldistributionsystem for areceiver of multi-channel pulsetrains in which indiv-idual trains Ofsignal pulses, the pulses of 30signals inserted at regular intervals in said multichannel train, saidmarker signals each consisting of two adjacent pulses spaced moreclosely together than any other two pulses in said multichannel train;`a' marker signal separator comprising a storage device, 'means forapplying each of the pulses of the multi-channel train to sequentiallycharge said device, means for delaying the multi-channel train for aperiod greater than the period between the two adjacent pulses of themarker signal and less than the period between any other two pulses ofthe train, means for applying the delayed pulses to each discharge saidstorage device whereby the periodic voltage built up on said storagedevice by the marker pulses of the undelayed train are greater than thecorresponding voltage of the signal pulses, and a threshold devicecoupled to said storage device having a 'threshold level above saidcorresponding voltage and below said periodic voltage whereby the markersignal is selected.

LESTER DUBIN.

REFERENCES CITED The following references are of record inthe le of thispatent:

UNITED STATES PATENTS Number Name Date 1 2,405,069 Tonks July 30, 19,462,419,340 Easton Apr. 22, 1947 2,485,591 Grieg Oct. 25, 1949

